Among semiconductor wafer defects (structural or chemical abnormalities which detract from an ideal crystal structure in the surface layer of a semiconductor wafer), those defects which can be the cause of semiconductor device failure are called “killer defects”. In the case of an epitaxial wafer, convex-shape SFs (Stacking Faults) and mounds have long been known as typical killer defects. Optical scattering methods are widely used as methods to detect such defects (see for example Japanese Patent Laid-open No. 2001-176943). According to the inspection method described in Japanese Patent Laid-open No. 2001-176943, a foreign matter inspection apparatus using an light scattering method (for example, KLA-Tencor's Surfscan 6200 (a registered trademark)) is used to irradiate the surface of the epitaxial wafer with a laser beam, the sizes of laser light scatterers existing on the wafer surface are measured, and laser light scatterers are judged to be stacking faults when their measured size exceed a prescribed value.
On the other hand, in recent years it has been found that broad flat defects the height of which is extremely low, ranging from several nanometers to several tens of nanometers, and the length-direction dimensions of which extend to several hundreds of microns, also rarely exist on the surface of epitaxial wafers. This type of defect is called a LAD (Large Area Defect). LADs are also “killer defects”; it has been reported that a LAD can result in defocus failures in semiconductor device manufacturing processes, and can cause degeneration of oxide film breakdown voltages and lifetimes.
While in general many of the killer defects other than LADs have heights of order ranging from several hundred nanometers to several hundred microns, the heights of LADs are, as explained above, extremely low, from nanometer order to several tens of nanometers. Because of these low heights, it is difficult to discover LADs using light scattering methods. And even when a LAD is discovered using a light scattering method, it is extremely difficult to differentiate a LAD from other laser light scatterers, such as for example particles or others defects on the wafer surface.
In Toshiya Sato et al, “Epitakisharu ueha ni okeru LAD no eikyou” (Effects of LADs on epitaxial wafers), pp. 35-40, Japan Soc. Applied Physics, Silicon Technology Division, No. 16, Apr. 24, 2000, it is reported that a foreign matter inspection apparatus using a light scattering method (for example, ADE's AWIS (a registered trademark)) can be used to differentiate LADs and particles (dust and other foreign matter on the wafer surface). According to this report, a laser beam is made obliquely incident on the wafer surface, P polarized light and S polarized light scattered from the surface are measured, and based on the intensities of both the P polarized light and the S polarized light, it is possible to judge whether a laser light scatterer on the wafer surface is a LAD or a particle.
In the method of Toshiya Sato et al, “Epitakisharu ueha ni okeru LAD no eikyou”, pp. 35-40, Japan Soc. Applied Physics, Silicon Technology Division, No. 16, Apr. 24, 2000, scanning of the wafer surface must be repeated twice when measuring P polarized light and S polarized light, so that throughput is low. Moreover, when using this method, there is anticipated the further difficulty that, if the height or other parameters of a LAD are different, the judgment conditions applied to the intensities of the P polarized light and S polarized light must also be changed.
Hence an object of this invention is to enable detection of LADs on a semiconductor wafer and discrimate LADs from other laser light scatterers.
A further object is to enable detection of LADs on a semiconductor wafer in a single scanning operation.